Aluminoxane modification

ABSTRACT

A modified aluminoxane is disclosed. Aluminoxane compounds are modified with glycol ethers or polyethers. The modified aluminoxanes are effective activators for single-site catalysts. Catalyst activated with the modified aluminoxane produces polyolefin with increased melt flow index, broadened molecular weight distribution, and improved thermal processability.

FIELD OF THE INVENTION

The invention relates to modification of aluminoxane. More particularly,the invention relates to modification of aluminoxane with glycol etheror polyether.

BACKGROUND OF THE INVENTION

Single-site catalysts are known. They can be divided into metallocenesand non-metallocenes. Metallocene single-site catalysts are transitionmetal compounds that contain cyclopentadienyl (Cp) or Cp derivativeligands. Non-metallocene single-site catalysts contain ligands otherthan Cp but have similar catalytic characteristics to the metallocenes.The non-metallocene single-site catalysts often contain heteroatomicligands, e.g., boraary, pyrrolyl, azaborolinyl, indenoindolyl andquinolinyl.

Aluminoxane compounds are activators for single-site catalysts. Thereare many ways to make aluminoxane compounds. For instance, aluminoxanescan be produced by contacting a trialkylaluminum compound with water.See U.S. Pat. No. 5,041,585. Commonly used aluminoxane is methylaluminoxane (MAO) or its derivatives.

Methods for modifying aluminoxanes are known. For instance, U.S. Pat.No. 6,340,771 teaches modifying MAO with sugar to make “sweet” MAO.Also, U.S. Pat. No. 5,543,377 teaches modifying aluminoxane compoundswith ketoalcohols and β-diketones.

Single-site catalysts produce polyolefin having narrow molecular weightdistribution. The uniformity of molecular weight distribution ofsingle-site polyolefin, although improving tensile strength and otherphysical properties of polymer products, makes the thermal processingdifficult. Many methods have been developed to improve processability ofsingle-site polyolefin. U.S. Pat. No. 6,127,484, for example, teaches amultiple-zone, multiple-catalyst process for making polyethylene. Thepolymer produced has a broad molecular weight distribution and improvedprocessability.

New methods for modifying aluminoxane compounds are needed. Ideally, themethod would be inexpensive and easy to practice. Particularly, themodified aluminoxane would increase molecular weight distribution andimprove the processability of single-site polyolefin.

SUMMARY OF THE INVENTION

The invention is a modified aluminoxane. The modified aluminoxane isprepared by treating an aluminoxane compound with glycol ether orpolyether. The invention also provides a catalyst system for olefinpolymerization. The catalyst system comprises the modified aluminoxaneand a transition metal complex. The catalyst system produces polyolefinthat has increased melt flow index, broadened molecular weightdistribution, and improved thermal processability.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a modified aluminoxane. The modified aluminoxane isprepared by treating an aluminoxane compound with glycol ether orpolyether. By “treating,” we meant either chemically reacting orphysically mixing, or both.

Suitable aluminoxane compounds include linear aluminoxanes having theformula:

R¹ ₂AlO(R²AlO)_(n)AlR³ ₂

R¹, R², and R³ are independently selected from the group consisting ofC₁₋₂₀ hydrocarbyl radicals and n is from 0 to 50. Preferably, R¹, R²,and R³ are methyl group. Preferably, n is from 0 to 10.

Suitable aluminoxane compound also includes cyclic aluminoxanes having arepeating unit of

—[Al(R⁴)—O]—

R⁴ is a C₁₋₂₀ hydrocarbyl. Preferably, R⁴ is methyl group.

Suitable glycol ethers include monoalkyl and dialkyl ethers of ethyleneglycol, propylene glycol, diethylene glycol, dipropylene glycol,1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, cyclohexane-1,4-dimethanol, neopentylglycol, and mixtures thereof. Examples of suitable glycol ethers areethylene glycol monomethyl ether, ethylene glycol dimethyl ether,ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethyleneglycol monopropyl ether, ethylene glycol dipropyl ether, ethylene glycolmonobutyl ether, ethylene glycol dibutyl ether, propylene glycolmonomethyl ether, propylene glycol dimethyl ether, propylene glycolmonoethyl ether, propylene glycol diethyl ether, propylene glycolmonopropyl ether, propylene glycol dipropyl ether, propylene glycolmonobutyl ether, propylene glycol dibutyl ether, the like, and mixturesthereof. Preferably, the glycol ethers are monoalkyl ethers.

Suitable polyethers include polyethylene glycol, polyethylene glycolmonoalkyl ethers, polyethylene glycol dialkyl ethers, polypropyleneglycol, polypropylene glycol monoalkyl ethers, polypropylene glycoldialkyl ethers, the like, and mixtures thereof. Polyethers also includeglycol ethers which have more than two glycol units, such as triethyleneglycol, tripropylene glycol, and their mono- and dialkyl ethers.

The treatment can be carried out at a temperature from 0° C. to 200° C.Preferably, the temperature is from 20° C. to 40° C. The weight ratio ofglycol ether or polyether to aluminoxane may be from 1:500 to 5:1,preferably from 1:100 to 1:1. Generally, the treatment takes place in aninert diluent or solvent, preferably under an inert atmosphere such asnitrogen. Suitable diluents and solvents include aliphatic and aromatichydrocarbons, ethers, esters, and ketones. After the treatment, diluentsand solvents may be removed.

Glycol ether- or polyether-treated aluminoxane compounds are activatorsfor single-site catalysts. Single-site catalysts suitable for use in thepresent invention include transition metal complex having the generalformula:

(L)_(n)—M—(X)_(m)

M is a transition metal. Preferably, M is Zr, Ti, or Hf. Morepreferably, M is Zr.

X is an activatable ligand. “Activatable ligand” means a ligand which isable to be activated by the treated aluminoxane to facilitate olefinpolymerization. X is independently selected from the group consisting ofhydrogen, halides, C₁₋₁₀ hydrocarbyls, C₁₋₁₀ alkoxys, and C₅₋₁₀aryloxys. The hydrocarbyl, alkoxy, and aryloxy ligands may also besubstituted, for example, by halogen, alkyl, alkoxy, and aryloxy groups.Preferably, X is a halide. More preferably, X is chloride.

L is a ligand preferably selected from the group consisting ofcyclopentadienyl, boraary, pyrrolyl, azaborolinyl, quinolinyl,indenoindolyl, and phosphinimine, the like, and mixtures thereof. Theseligands provide the catalysts with “single-site” nature. That is, thecatalyst has only one active site for olefin polymerization and thusprovides the polyolefin with relatively narrow molecular weight andcomposition distributions.

Cyclopentadienyl ligands include substituted cyclopentadienyl such asmethyl, isopropyl, and butyl cyclopentadienyl ligands. Cyclopentadienylligands also include substituted and non-substituted indenyl andfluorenyl ligands. Cyclopentadienyl based single-site catalysts areknown, see, e.g., U.S. Pat. Nos. 4,404,344, 4,769,510, 6,160,066, and5,955,625, the teachings of which are incorporated herein by reference.

Boraary, pyrrolyl, azaborolinyl, quinolinyl, and phosphinimine basedsingle-site catalysts are also known, see, e.g., U.S. Pat. Nos.6,034,027, 5,539,124, 5,756,611, 5,637,660, 6,340,771, and 6,350,831,the teachings of which are incorporated herein by reference. Theseheteroatom-containing can also be substituted.

Numbers n and m depend on the valence of the transition metal. The sumof n and m equals to the valence of the metal. Number n is preferably 1or greater.

Two L ligands can be bridged. Groups that can be used to bridge theligands include, for example, methylene, ethylene, 1,2-phenylene, anddialkyl silyls. Examples are —CH₂—, —CH₂—CH₂—, and —Si(CH₃)₂—. Bridgingchanges the geometry around the transition metal and can improvecatalyst activity and other properties such as comonomer incorporation.

The catalyst may be immobilized on a support. The support is preferablya porous material such as inorganic oxides and chlorides, organicpolymer resins, and mixtures thereof. Preferred inorganic oxides includeoxides of Group 2, 3, 4, 5, 13, or 14 elements. Preferred supportsinclude silica, alumina, silica-aluminas, magnesias, titanias,zirconias, magnesium chloride, clay, and crosslinked polystyrene. Silicais most preferred.

Preferably, the support has a surface area in the range of about 10 toabout 700 m²/g, a pore volume in the range of about 0.1 to about 4.0mL/g, an average particle size in the range of about 5 to about 500 μm,and an average pore diameter in the range of about 5 to about 1000 Å.They are preferably modified by heat treatment, chemical modification,or both. For heat treatment, the support is preferably heated at atemperature from about 50° C. to about 1000° C. More preferably, thetemperature is from about 50° C. to about 600° C.

Suitable chemical modifiers include organoaluminum, organosilicon,organomagnesium, and organoboron compounds. Organosilicon andorganoboron compounds, such as hexamethyl-disilazane and triethylborane,are preferred. Suitable techniques to support a single-site catalyst aretaught, for example, in U.S. Pat. No. 6,211,311, the teachings of whichare incorporated herein by reference.

Polymerization is conducted in the presence of the treated aluminoxaneand a single-site catalyst. It can be conducted in bulk, gas phase orslurry phase. Methods and apparatus for gas phase polymerization ofethylene with Ziegler catalysts are well known, and they are suitablefor use in the process of the invention. For example, U.S. Pat. No.5,859,157, the teachings of which are herein incorporated by reference,teaches in detail a gas phase polymerization of ethylene with a Zieglercatalyst. The slurry-phase polymerization is performed in an organicsolvent that can disperse the catalyst and polyolefin. Suitable solventsinclude C₄ to C₁₀ linear, branched, and cyclic aliphatic, and C₆-C₁₂aromatic hydrocarbons. Examples of suitable solvents are butane, hexane,cyclohexane, octane, heptane, isobutene, toluene, and mixtures thereof.

The polymerization is preferably conducted under pressure. The pressureis preferably in the range of about 50 to about 15,000 psi, morepreferably from about 100 to about 5,000 psi, and most preferably fromabout 200 to about 2,000 psi. Generally, the higher the pressure, themore productive the process. Laboratory operations are conducted underrelatively low pressure for safety reasons. Polymerization is preferablyconducted at a temperature below 100° C. More preferably, thetemperature is within the range of about 50° C. to about 90° C.

A scavenger is preferably used in the polymerization. Scavengers reducethe effect of a trace amount of moisture and oxygen existing in thereactor on the polymerization and increase the activity and lifetime ofthe catalysts. Suitable scavengers include alkyl aluminum compounds.Scavengers are added into the reactor prior to the addition of catalyst.The amount of scavengers is about 1 to 2000 times in mole of thecatalyst.

Suitable olefins for the polymerization include C₂₋₁₀ α-olefins, cyclicolefins, dienes, and mixtures thereof. Examples are ethylene, propylene,1-butene, 1-hexene, cyclopetene, and isoprene.

We have found that using the treated aluminoxane of the invention with asingle-site catalyst can effectively increase melt flow index, broadenthe molecular weight distribution of polyolefin, and therefore improvesthe thermal processability of the polymer. Further, using the treatedaluminoxane of the invention introduces glycol ether or polyethercomponent into olefin polymerization. These polar compounds can functionas antistatic agents to reduce reactor fouling. Many other advantages ofthe invention are also expected.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLE 1 Polymerization of Ethylene With Propylene Glycol Methyl Ether(PGME)-Modified Methylaluminoxane (MAO)

Step I. Modification of MAO With PGME

In an inert atmosphere glovebox, MAO (4 mL of 30 weight percent MAO intoluene solution, product of Albemarle) is mixed with 37 mg of PGME(product of Aldrich). The mixture is stirred for 30 minutes, and themodified MAO is used for the next step.

Step II. Immobilization of Modified MAO on Support

Silica (Davison G955) is calcined at 250° C. for 12 hours and thencooled to room temperature. In an inert atmosphere glovebox, 5 grams ofthe calcined silica is mixed with the above modified MAO. After stirringthe mixture for about 30 minutes, the toluene is removed by vacuum andthe treated silica is then dried in vacuum (about 28.5 inches mercury)at room temperature for about 3 hours.

Step III. Preparation of Supported Catalyst

In an inert atmosphere glovebox, MAO (1.12 mL, 30 weight percent MAO intoluene solution, purchased from Albemarle) is diluted with toluene (2.3mL). Dimethylsilyl-bridged indeno[2,1-b]indolyl cyclopentadienylzirconium dichloride (53.0 mg) is added to the solution. The product ofstep II (1.27 g) is added to the solution. The mixture is stirred for anadditional 30 minutes and then dried by vacuum (about 28.5 inchesmercury) at room temperature for about 2 hours. About 1.70 g of eachfinal supported catalyst is obtained.

Step IV. Polymerization

A one-liter, stainless-steel reactor is charged with 1-hexene (75 mL),and triisobutylaluminum (1.0 mL of 1.0 M solution in heptane, 1.0 mmol).Hydrogen is added (100 psig from a 10-mL stainless-steel cylinderpressurized initially to about 670 psig H₂) to the reactor, which isthen pressurized with ethylene to 375 psig. The reactor contents heatedat 75° C., and then the supported catalyst of step III (19 mg) isflashed into the reactor with about 50 mL of isobutane. Thepolymerization proceeds for 0.5 hour. The reactor is vented and thepolymer is collected and dried by vacuum. The polymer has aweight-average molecular weight (Mw): 91,500, molecular weightdistribution (Mw/Mn): 3.6, melt index (MI): 2.7, and density 0.914 g/mL.

EXAMPLE 2 Polymerization of Ethylene With Polypropylene Glycol(PPG)-Modified MAO

Step I. Modification of MAO With PPG

In an inert atmosphere glovebox, MAO (4 mL of 30 weight percent MAO intoluene solution) is mixed with 175 mg of PPG (average Mn of about 425,product of Aldrich). The mixture is stirred for 30 minutes. The modifiedMAO is used for the next step.

Step II. Immobilization of Modified MAO on Support

Silica (Davison G955) is calcined at 250° C. for 12 hours before coolingto room temperature. In an inert atmosphere glovebox, 5 grams of thecalcined silica is mixed with the above modified MAO. After stirring forabout 30 minutes, the toluene is removed by vacuum from the mixture andthe treated silica is then dried in vacuum (about 28.5 inches mercury)at room temperature for about 3 hours.

Step III. Preparation of Supported Catalyst

In an inert atmosphere glovebox, MAO (1.12 mL, 30 weight percent MAO intoluene solution, purchased from Albemarle) is diluted with toluene (2.3mL). Dimethylsilyl-bridged indeno[2,1-b]indolyl cyclopentadienylzirconium dichloride (53.0 mg) is added to the solution. The product ofstep III (1.27 g) is added to the solution. The mixture is stirred foran additional 30 minutes and then dried by vacuum (about 28.5 inchesmercury) at room temperature for about 2 hours. About 1.70 g of eachfinal supported catalyst is obtained.

Step IV. Polymerization

The polymerization procedure of Example 1 is repeated, but the abovesupported catalyst containing PPG-modified, rather than PGME-modified,MAO is used. The polymer has Mw: 82,100, Mw/Mn: 3.3, MI: 4.05, anddensity: 0.912 g/mL.

COMPARATIVE EXAMPLE 3 Polymerization of Ethylene With Unmodified MAO

Polymerization procedure of Example 1 is repeated, but no modified MAOis used. The polymer has Mw: 96,000, Mw/Mn: 2.8, MI: 0.95, and density:0.908 g/MI.

Compared with unmodified MAO, the polymers made with eitherPGME-modified or PPG-modified MAO has significantly increased Mw/Mn andMI. The results are listed in Table 1.

TABLE 1 Density, Example MAO modifier Mw Mw/Mn MI g/mL 1 Propyleneglycol 91,500 3.6 2.7 0.914 methyl ether 2 Polypropylene glycol 82,1003.3 4.05 0.912 C3 None 96,000 2.8 0.95 0.908

We claim:
 1. A modified aluminoxane comprising an aluminoxane compoundand a polyether having more than three of glycol units.
 2. The modifiedaluminoxane of claim 1 wherein the polyether is selected from the groupconsisting of polyethylene glycol, polyethylene glycol monoalkyl ethers,polyethylene glycol dialkyl ethers, polypropylene glycol, polypropyleneglycol monoalkyl ethers, and polypropyllene glycol dialkyl ethers. 3.The modified aluminoxane of claim 1 wherein the aluminoxane compound hasthe general formula: R¹ ₂AlO(R²AlO)_(n)AlR³ ₂ wherein each R¹, R², andR³ is independently a C₁₋₂₀ hydrocarbyl and n is from 0 to
 50. 4. Themodified aluminoxane of claim 1 wherein the aluminoxane compound is acyclic aluminoxane having a repeating unit of —[Al(R⁴)—O]— wherein R⁴ isa C₁₋₂₀ hydrocarbyl.